Move 'reserved clients' stuff to runtime, since 'ulimit -n' could be lower.

This fixes a bug where if you run ./Config with 'auto' file descriptors,
and then have an unusually low 'ulimit -n' of like 150, you would end up
with a negative amount of file descriptors available for use.

This fix moves it from compile-time setting of reserved fd's to runtime
setting.

All this is wrong, by the way, but that is for another major overhaul,
at least this bug is fixed now :D

doc/RELEASE-NOTES.md

@@ -11,6 +11,9 @@ in progress and may not always be a stable version.
 * TODO
 
 ### Fixes:
+* If your shell only allowed very few file descriptors (eg: `ulimit -n`
+  returned `150`), then UnrealIRCd would fail to boot. This, because due to
+  reserved file descriptors you would have 0 left, or even a negative number.
 * +I ~operclass was not working properly.
 
 ### Developers and protocol:

include/config.h

@@ -173,21 +173,6 @@
  #endif
 #endif
 
-/* Number of file descriptors reserved for non-incoming-clients.
- * One of which may be used by auth, the rest are really reserved.
- * They can be used for outgoing server links, listeners, logging,
- * DNS lookups, HTTPS callbacks, etc.
- */
-#if MAXCONNECTIONS >= 10000
- #define CLIENTS_RESERVE 250
-#elif MAXCONNECTIONS >= 2048
- #define CLIENTS_RESERVE 32
-#elif MAXCONNECTIONS >= 1024
- #define CLIENTS_RESERVE 16
-#else
- #define CLIENTS_RESERVE 8
-#endif
-
 /*
  * this defines the length of the nickname history.  each time a user changes
  * nickname or signs off, their old nickname is added to the top of the list.

include/h.h

@@ -1135,6 +1135,7 @@ extern void concat_params(char *buf, int len, int parc, const char *parv[]);
 extern void charsys_check_for_changes(void);
 extern void dns_check_for_changes(void);
 extern MODVAR int maxclients;
+extern MODVAR int reserved_fds;
 extern int fast_badword_match(ConfigItem_badword *badword, const char *line);
 extern int fast_badword_replace(ConfigItem_badword *badword, const char *line, char *buf, int max);
 extern const char *stripbadwords(const char *str, ConfigItem_badword *start_bw, int *blocked);

src/ircd.c

@@ -801,7 +801,7 @@ int InitUnrealIRCd(int argc, char *argv[])
 #ifndef _WIN32
 	fprintf(stderr, "\n");
 	fprintf(stderr, "This server can handle %d concurrent sockets (%d clients + %d reserve)\n\n",
-		maxclients+CLIENTS_RESERVE, maxclients, CLIENTS_RESERVE);
+		maxclients+reserved_fds, maxclients, reserved_fds);
 #endif
 	init_CommandHash();
 	initwhowas();

src/modules/stats.c

@@ -900,7 +900,7 @@ int stats_set(Client *client, const char *para)
 	RunHook(HOOKTYPE_STATS, client, "S");
 #ifndef _WIN32
 	sendtxtnumeric(client, "This server can handle %d concurrent sockets (%d clients + %d reserve)",
-		maxclients+CLIENTS_RESERVE, maxclients, CLIENTS_RESERVE);
+		maxclients+reserved_fds, maxclients, reserved_fds);
 #endif
 	return 1;
 }

src/socket.c

@@ -135,7 +135,7 @@ static int listener_accept_wrapper(ConfigItem_listen *listener)
 	if (listener->options & LISTENER_CONTROL)
 	{
 		/* ... but not unlimited ;) */
-		if ((++OpenFiles >= maxclients+(CLIENTS_RESERVE/2)) || (cli_fd >= maxclients+(CLIENTS_RESERVE/2)))
+		if ((++OpenFiles >= maxclients+(reserved_fds/2)) || (cli_fd >= maxclients+(reserved_fds/2)))
 		{
 			ircstats.is_ref++;
 			if (last_allinuse < TStime() - 15)
@@ -430,7 +430,15 @@ void close_all_listeners(void)
 		close_listener(aconf);
 }
 
-int maxclients = 1024 - CLIENTS_RESERVE;
+/* First, set these up for maxclients 1024 with a reserve of 16,
+ * this is adjusted at boot time, though, it is just for an
+ * initial value!
+ */
+
+/** Number of file descriptors reserved */
+int reserved_fds = 16;
+/** Maximum number of regular clients */
+int maxclients = 1024 - 16;
 
 /** Check the maximum number of sockets (users) that we can handle - called on startup.
  */
@@ -473,7 +481,7 @@ void check_user_limit(void)
 			                m);
 			exit(-1);
 		}
-		maxclients = m - CLIENTS_RESERVE;
+		maxclients = m;
 	}
 #endif // RLIMIT_FD_MAX
 
@@ -489,8 +497,20 @@ void check_user_limit(void)
 #endif
 #endif
 #ifdef _WIN32
-	maxclients = MAXCONNECTIONS - CLIENTS_RESERVE;
+	maxclients = MAXCONNECTIONS;
 #endif
+
+	/* Now adjust the 'reserve', this was previously in config.h */
+	if (maxclients >= 10000)
+		reserved_fds = 250;
+	else if (maxclients >= 2048)
+		reserved_fds = 32;
+	else if (maxclients >= 1024)
+		reserved_fds = 16;
+	else
+		reserved_fds = 8;
+
+	maxclients -= reserved_fds;
 }
 
 /** Initialize some systems - called on startup */